Field of Invention
This invention relates generally to toy vehicles driven by a DC motor energized by a battery supply, and more particularly to a vehicle of this type in which a single light bulb is disposed at the optical inlet of a plastic light guide contoured to define light outlets in the form of a pair of simulated front headlights and a bank of simulated dashboard and gear shift indicators.
Toy vehicles which are driven by a small DC motor operated by a battery are commonplace. It is also known in toy vehicles to use the battery power supply to energize headlight bulbs. And in order to avoid the need for a separate light bulb in each dashboard indicator, it is known to use a common light bulb whose light is directed to a plurality of dashboard indicators by way of optical fibers or light pipes.
One can transmit light from one end of a long glass cylinder to the other without leakage, provided that the light strikes the wall of the cylinder with an angle of incidence greater than the critical angle for total internal reflection. In transmission, light travels through the cylinder in a zig-zag path of successive internal reflections. To convey light without reflection loss, it is necessary that the angle of incidence A exceed the critical angle as expressed by the equation Sin A=N.sub.2 /N.sub.1 ; where N.sub.1 is the refractive index of the transmission material and N.sub.2 that of the outer medium which in the case of a glass cylinder is air.
It is also possible to guide light through a clear plastic block formed of acrylic or other glass-like material, for the index of refraction of this material relative to that of air results in internal reflection. The present invention exploits the optical light guide characteristics of such plastic blocks to provide illumination for simulated headlights and dashboard and gear shift light indicators in a toy vehicle.